We present in this paper a modeling approach of the pedagogical sequencing of learning units which is called a PGM Pedagogical Graph Model. This graph allows expressing the totality of the pedagogical constraints. PGM is a graph in which the nodes are the learning units and the arcs are the pedagogical constraints between learning units. This will help the author to well structure his/her course and pedagogical relations between the various pedagogical units that compose it and help the learner to be oriented during the browsing in the course avoiding thus the disadvantages of the hypertext links.